Several sports, such as tennis, baseball, softball, volleyball, among others, require a player to hit a ball either with a racquet, a bat, or their hand. Players often practice hitting the ball. Generally, two players are necessary to practice these sports. One player throws the ball, and another player catches the ball or hits the ball back to the first player. Sometimes, a player wants to practice hitting a ball and does not have another player to throw the ball. Therefore, if a player wants to improve his or her ball hitting skills, a player needs the assistance of another player and cannot play by himself or herself. Moreover, the other player might not be skilled in the game and might lack the techniques of throwing the ball correctly.
Tennis is usually an individual sport where two teams play against each other. Each team may include a single player (singles) or two players (doubles). The object of the game is for each player to play the ball in such a way that the opponent is not able to play a good return. Each player has a racquet strung with cord to strike a ball thrown by the opponent. The ball is usually a hollow rubber ball covered with felt. Each player stands on one side of a net that divides a court, and the ball is thrown between the players over the net. In tennis, the serve is generally the most challenging part of the game. The tennis serve consists of a player throwing the ball in the air and swinging the racquet toward the opponent on the other side of the court.